CBSE Class 10 Science 2017 · Paper 531 · Question 20

(a) A: pollen grain (germinating on the stigma); B: pollen tube; C: ovary; D: female germ-cell (egg) inside the ovule. (b) Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a flower; within the same flower it is self-pollination, and from one flower to another it is cross-pollination. Significance: it brings the male germ-cells to the female part of the flower, so that fertilisation, and then the formation of seeds and fruit, can take place; cross-pollination between flowers of different plants also brings together germ-cells from two parents and so gives variation among the offspring. (c) A pollen grain on a suitable stigma grows a pollen tube, which passes through the style and reaches the ovule in the ovary. The male germ-cell travels down the tube and fuses with the female germ-cell (egg) inside the ovule; this is fertilisation, and it forms a zygote, which divides to form the embryo. After fertilisation (i) the ovules develop into seeds and (ii) the ovary develops into the fruit.